Process of depositing ferromagnetic compositions



United States Patent 3,219,471 PRLCESS 0F DEPOSITING FERROMAGNETIC COMEPGSETIONS Wiiiiam H. Chiiton and Robert D. Fisher, Dayton, Ohio, assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland No Drawing. Filed Sept. 14, 1961, Ser. No. 137,965 9 Claims. (CE. 11747) The present invention relates generally to the process of fabricating magnetic data-storage devices, and more specifically relates to a new and improved process for fabricating magnetic devices of the high density storage type which are readily adaptable for use in present-day electronic computers and data processors.

It is a general object of the present invention to devise a new and improved process whereby magnetic data storage devices of the high density storage type are fabricated in a simple and economical manner, and which possess greatly improved magnetic and other characteristics than heretofore possible.

A more specific object of the present invention is to devise a new and improved chemical deposition process capable of producing magnetic data-storage devices which possess highly desirable characteristics such as: a magnetic coercivity greater than 200 oersteds; a substantially rectangular magnetic hysteresis loop; and having substantially uniform physical and magnetic properties, in addition to high resistance to physical wear.

In accordance with the present invention, there has been devised a new and improved process for fabricating new and improved magnetic data-storage devices of the high density storage type. Such a process comprises the steps of first providing a catalytically active substrate capable of receiving a metallic deposit thereon by the process of chemical reduction. Thereafter, the catalytically active substrate is immersed in a complexed aqueous solution having a pH in the alkaline range and including as essential constituents cobalt and hypophosphite ions. During deposition, the combined concentration of cobalt and hypophosphite ions is maintained substantially constant in the range of 2.0 to 8.2 grams/liter, and, additionally, the ratio of cobalt ion concentration to hypophosphite ion concentration is maintained substantially constant in the range of .2 to 1.7. The substrate is maintained in the solution for a time sufficient to effect chemical reduction of a cobalt deposit on the surface thereof having a coercive force of at least 200 oersteds. The cobalt coated substrate is thereafter rinsed and dried and is then ready to be incorporated in present day electronic computers and data processors as a data storage device.

The particular substrate onto which the desired cobalt coating is to be chemically deposited may be any of the various shapes and sizes presently being utilized by the computer industry and may either be metallic or nonmetaliic. However, in order to fabricate a storage device in accordance with applicants intended uses, it is preferred that the substrate be a relatively thin sheet or ribbon of polyethylene terephthalate, commonly sold under the trademark Mylar, having a thickness in the order of 0.003 inch.

To insure uniform chemical reduction throughout the entire surface area of the substrate, it is preferred that the substrate first be rigorously cleaned by immersion in a one molar concentration sodium hydroxide solution, followed by a thorough rinsing in distilled water, a subsequent immersion in a 1/1 dilution of hydrochloric acid solution, again followed by a thorough rinsing in distilled water, and thereafter thoroughly rinsed in acetone. Even though a specific cleaning operation is shown and described, it is, of course, to be appreciated that any of the 3,219,47 i Patented Nov. 23, 1965 well known alkaline-acid cleaning procedures may be used with equal success.

In order to improve adhesion of the cobalt coating on the supporting substrate, it is preferred that the substrate next be coated with a suitable commercially available adhesive prior to deposition of metallic cobalt thereon. While any of the various commercially available adhesives may be used with equal success, it is preferred that the adhesive be prepared by mixing one part of Shipleys No. ZOOTF adhesive, currently manufactured by the Shipley Company, Inc., of Wellesley, Massachusetts, United States of America, with three parts of methyl ethyl ketone. Shipleys No. ZOOTF adhesive is a well-known Buna-N type adhesive consisting essentially of a thermo plastic base of nitrile-rubber and a small amount of a phenolic thermosetting resin. The substrate is then dipped into the adhesive solution and slowly withdrawn at a rate of approximately 0.33 inch/second, then air dried for approximately 30 minutcs, and thereafter cured for approximately 10 hours at a temperature of approximately degrees centigrade. It is to be noted that the particular manner of applying the adhesive coating to the supporting substrate is not critical; the only restriction is that the adhesive coating be uniformly distributed on the surface thereof.

As is well known to those skilled in the art of chemical deposition, chemical reduction of metallic ions is essentially a controlled autocatalytic reduction process of the depositing species on an active metal such as aluminum, iron, nickel, cobalt, palladium, and the like, in the presence of hypophosphite ions; non-active metals such as copper and alloys thereof are normally activated by immersion deposition of palladium onto the depositing surface thereof. However, in the case of non-conducting materials, (such as the mentioned Mylar) activation is normally accomplished by chemical or vacuum deposition thereon of either a copper or a silver film, followed by immersion deposition of palladium onto the surface of the film. It is preferred, however, that the substrate be activated by first being immersed in a stannous chloride solution whereby stannous ions are adsorbed on the surface thereof. Thereafter, the substrate is immersed in a palladium chloride solution whereby the palladium ions in solution are spontaneously reduced by the adsorbed stannous ions, thereby rendering the substrate catalytical- 1y active.

Therefore, it is preferred that the adhesive coated Mylar substrate be activated by immersion for a period of ap proximately 5 minutes in a 20 gram/liter aqueous stannous chloride solution containing approximately 10 milliliters/ liter of concentrated hydrochloride acid, with the temperature of the stannous chloride solution being maintained substantially constant at approximately 25 degrees centigrade. Thereafter, the substrate is immersed for a period of approximately 5 minutes in an aqueous palladium chloride solution having a concentration of approximately 0.5 gram/liter and containing approximately 5 milliliters of concentrated hydrochloric acid per liter of solution, with the temperature of the palladium chloride solution being maintained substantially constant at approximately 25 degrees centigrade.

Following the just-described activation operation, the final step in the present process is the immersion of the thus activated substrate in an aqueous solution having constituent concentrations in accordance with the teacl1 ings of the present invention.

As evidenced by United States Patents 2,430,581 and 2,532,284, and also by British Patent 749,824, chemical reduction of cobalt ions effected by the presence in the solution of hypophosphite ions is a well-known autocatalytic reduction phenomenon which has been utilized for some time in chemical deposition of metallic cobalt for tarnish and corrosion resistance purposes. W

Applicants, however, have discovered that it is possible to obtain cobalt deposits having extraordinary magwithin the range of 55 degrees centigrade to 90 degrees Centigrade, preferably 80 degrees centigrade, and the pH thereof is maintained substantially constant within the range of 7.0 to 9.0, preferably 8.2, by means of a perinetic and physical properties if the total concentration 5 staltic action pump through which sodium hydroxide is of cobalt and hypophosphite ions, in addition to the continuously added. Following preparation of the plating ratio of cobalt ion concentration to hypophosphite ion solution, the activated, adhesive coated, Mylar substrate concentration, are both maintained substantially conis immersed therein for a period of approximately one stant within certain prescribed ranges during the deposihour. Upon emergence from the plating solution, the tion process, all of which to the knowledge of applicants thus coated substrate is rinsed and dried and is then ready have not heretofore been recognized by those skilled in to be utilized in a well-known manner as a high density the art of chemical deposition. magnetic data-storage device.

In the following chart, for each of illustrative baths It should now be clearly evident that applicants have 1 through 6, the concentration of the actual compounds devised a simple and economical process of fabricating dissolved in the plating solution measured in grams/ new and improved magnetic data-storage devices of the liter of aqueous solution are listed in columns A through high storage density type which possess greatly improved D thereof, the respective concentrations in grams/liter magnetic and other characteristics than heretofore posof aqueous solution of cobalt ions and hypophosphite sible. ions present in solution as contributed by their respec- While particular embodiments of the present invention tive dissolved compounds are listed in columns E and F, have been shown and described, it will be obvious to the ratio of cobalt ion concentration to hypophosphite ion those skilled in the art of chemical deposition of magconcentration is listed in column G, the total concennetic compositions that changes and modifications may tration of cobalt and hypophosphite ions is listed in be made therein without departing from "the invention in column H, the value of the magnetic coercivity (Hc) its broader aspect, and, therefore, the aim of the appended of the resulting deposit is listed in column I, the value claims is to cover all such changes and modifications that of the remauent saturation (Br) is listed in column J, fall within the true spirit and scope of the invention. and the value of the saturation magnetization (B8) is What is claimed is: listed in column K. 1. The process of fabricating magnetic data-storage Bath composition Magnetic properties B th Compound concentrations" Cobalt-hypophosphite concentration a No.

GOC12'6H20, NttHgPOa-HgO, 11 0411 0711 0, NHrOl, Co++, H2PO2 C0++lHgPOr C0+++Hg H0, Br, BS,

g./l. g./l. g./l. g./l. g./l. g./1. POr g./l. oersteds gauss gauss *Sufficient sedium hydroxide (NaOH) to give pH in the range of 7-9, preferably 8.2, at 80 degrees centigrade.

As shown in the above chart, it has been discovered that, if the total concentration of cobalt ions and hypophosphite ions is maintained within the range of 5 2.0 to 8.2 grams/liter, preferably 4.0, and the ratio of cobalt ion concentration to hypophosphite ion concentration is maintained within the range of .2 to 1.7, preferably .86, metallic cobalt deposits are obtained having magnetic coercivity characteristics in the range of 288 to 319 oersteds, substantially rectangular magnetic hysteresis loop characteristics as determined by the quotient of the remanent magnetization and the saturation magnetization, and also possess substantially uniform physical and magnetic properties in addition to high resistance to physical wear.

Even though the particular type of complexing agent, or agents, employed may be any of the multitude well known to those skilled in the art, it is preferred that citric acid be utilized in an amount sufli-cient to supply citrate ions in a concentration at least equal to the concentration of cobalt ions utilized, whereby soluble cobalt complexes are formed thereby preventing precipitation of the cobalt ions. Additionally, it is preferred that ammonium ions be present in the plating solution of a concentration at least equal to .3 gram/liter of aqueous solution.

After the desired plating solution is prepared having the preferred constiuent concentrations in accordance with the teachings of the present invention, the operating temperature thereof is maintained substantially constant devices of the high density storage type, comprising the steps of:

providing a catalytically active substrate capable of receiving a metallic deposit thereon by chemical reduction;

immersing said substrate in a complexed aqueous solution having a pH in the alkaline range and including as essential constituents cobalt ions and hypophosphite ions, the combined concentration of said cobalt and hypophosphite ions being in the range of 2.0 to 8.2 grams/liter and the ratio of cobalt ion concentration to hypophosphite ion concentration being in the range of .2 to 1.7, all the metal plating ions consisting essentially of cobalt;

and maintaining said substrate in said solution for a time suflicient to effect chemical reduction of a cobalt deposit thereon.

2. A high density magnetic data-storage device fabricated in accordance with the process of claim 1.

3. The process of fabricating magnetic data-storage devices of the high storage density type, comprising the steps of:

providing a substrate having palladium on the surface thereof;

immersing said substrate in a complexed aqueous solution having a pH in the alkaline range and including as essential constituents cobalt ions and hypophosphite ions, the combined concentration of said cobalt and hyphophosphite ions being in the range of 2.0 to 8.2 grams/liter and the ratio of cobalt ion concentration to hypophosphite ion concentration being in the range of .2 to 1.7, all the metal plating ions consisting essentially of cobalt;

and maintaining said substrate in said solution for a time suflicient to efiect chemical reduction of a cobalt deposit thereon.

4. The process of fabricating magnetic data-storage devices of the high storage density type, comprising the steps of:

applying an adhesive coating to a non-metallic substrate;

catalytically activating the surface of the adhesive coated substrate with palladium;

immersing said substrate in a complexed aqueous solution having a pH in the alkaline range and including as essential constituents cobalt and hypophosphite ions, the combined concentration of said cobalt and hypophosphite ions being in the range of 2.0 to 8.2 grams/liter and the ratio of cobalt ion concentration to hypophosphite ion concentration being in the range of .2 to 1.7, all the metal plating ions consisting essentially of cobalt;

and maintaining said substrate in said solution for a time suflicient to effect chemical reduction of a cobalt deposit thereon.

5. The process of claim 3 in which said palladium is provided by immersing said substrate in a stannous chloride solution followed by immersion in a palladium chloride solution.

6. The process of claim 1 in which said solution additionally includes ammonium ions in a concentration of at least .3 gram/liter.

7. The process of claim 1 in which said solution includes citrate ions in a concentration at least equal to said cobalt ion concentration.

8. The process of fabricating magnetic data-storage devices of the high density storage type, comprising the steps of:

providing a catalytically active substrate capable of receiving a metallic deposit thereon by chemical reduction;

immersing said substrate in an aqueous solution having a pH in the range of 7 to 9 and including as essential constituents cobalt ions and hypophosphite ions, the combined concentration of said cobalt and hypophosphite ions being in the range of 2.0 to 8.2 grams/ liter and the ratio of cobalt ion concentration to hypophosphite ion concentration being in the range of .2 to 1.7, all the metal plating ions consisting essentially of cobalt and said solution further includ ing ammonium ions in a concentration of at least .3 gram/liter and citrate ions in a concentration at least equal to the concentration of said cobalt ions;

and maintaining said substrate in said solution for a time suiiicient to efiect chemical reduction of a cobalt deposit thereon.

9. The process of fabricating magnetic data-storage devices of the high density storage type, comprising the steps of:

applying an adhesive coating to a cleansed non-metallic substrate; immersing said substrate, first in an aqueous stannous chloride solution, and thereafter in an aqueous palladium chloride solution to thereby provide the surface of said substrate with palladium;

immersing the thus activated substrate in an aqueous solution having a pH approximately 8.2, a temperature approximately 80 degrees centigrade, and ineluding as essential constituents cobalt ions and hypophosphite ions, the combined concentration of said cobalt and hypophosphite ions being approximately 4 grams/liter and the ratio of cobalt ionic concentration to hypophosphite ionic concentration being approximately .9, all the metal plating ions consisting essentially of cobalt and said solution further including ammonium ions in a concentration of at least .3 gram/liter and citrate ions in a concentration at least equal to the cobalt ionic concentration;

and maintaining said substrate in said solution for a time suflicient to effect chemical reduction of a cobalt deposit on said substrate having a coercive force of at least 200 oersteds.

References Cited by the Examiner UNITED STATES PATENTS 2,430,581 11/ 1947 Pessell 117-227 2,532,283 12/ 1950 Brenner et al. 117-50 2,532,284 12/ 1950 Brenner et al. 117-50 2,917,439 12/1959 Liu 204-22 3,041,198 6/1962 Certa 117-130 3,116,159 12/1963 Fisher et al. 117-130 3,138,479 6/1964 Foley 117-130 FOREIGN PATENTS 749,824 6/ 1956 Great Britain.

OTHER REFERENCES Brenner et al., Deposition of Nickel and Cobalt by Chemical Reduction, Journal of Research of the National Bureau of Standards, volume 39, research paper RP 1835, pages 385-395, November 1947.

Tsu, IBM Technical Disclosure Bulletin, vol. 2, No. 3, page 36, October 1959.

Tsu et al., IBM Technical Disclosure Bulletin, vol. 4, No. 8, page 52, January 1962.

Symposium on Electroless Nickel Plating, ASTM Special Technical Publication No. 265, American Society ttor Testing Materials, Philadelphia 1959, pages 16, 34 and 36.

RICHARD D. NEVIUS, Primary Examiner.

JOSEPH B. SPENCER, Examiner. 

1. THE PROCESS FO FABRICATING MAGNETIC DATA-STORAGE DEVICES OF THE HIGH DENSITY STORAGE TYPE, COMPRISING THE STEPS OF: PROVIDING A CATALYTICALLY ACTIVE SUBSTRATE CAPABLE OF RECEIVING A METALLIC DEPOSIT THEREON BY CHEMICAL REDUCTION; IMMERSING SAID SUBSTRATE IN A COMPLEXED AQUEOUS SOLUION HAVING A PH IN THE ALKALINE RANGE AND INCLUDING AS ESSENTIAL CONSTITUENTS COBALT IONS AND HYPOPHOSPHITE IONS, THE COMBINED CONCENTRATION OF SAID COBALT AND HYPOPHOSPHITE IONS BEING IN THE RANGE OF 2.0 TO 8.2 GRAMS/LITER AND THE RATIO OF COBALT ION CONCONCENTRATION TO HYPOPHOSPHITE ION CONCENTRATION BEING IN THE RANGE OF .2 TO 1.7, ALL THE METAL PLATING IONS CONSISTING ESSENTIALLY OF COBALT; AND MAINTAINING SAID SUBSTRATE IN SAID SOLUTION FOR A TIME SUFFICIENT TO EFFECT CHEMICAL REDUCTION OF A COBALT DEPOSIT THEREON. 